Adaptive passive scanning and/or active probing techniques for mobile device positioning

ABSTRACT

Various methods, apparatuses and/or articles of manufacture are provided which may be implemented to support mobile device positioning through the use of adaptive passive scanning and/or adaptive active probing techniques. For example, a mobile device may acquire signals from wireless transceivers, identify wireless transceivers based, at least in part, on the acquired signal(s), determine a received signal strength measurement for each of the wireless transceivers based, at least in part, on the acquired signal(s), and determine a transmission power of a probe signal to be transmitted to at least one of the wireless transceivers based, at least in part, on at least one of the received signal strength measurements.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

This application claims priority under 35 USC 119 to U.S. ProvisionalApplication Ser. No. 61/661,760, filed Jun. 19, 2012, and entitled,“ADAPTIVE PASSIVE SCANNING AND/OR ACTIVE PROBING TECHNIQUES FOR MOBILEDEVICE POSITIONING”, which is assigned to the assignee hereof and whichis incorporated herein by reference.

BACKGROUND

1. Field

The subject matter disclosed herein relates to electronic devices, andmore particularly to methods, apparatuses and articles of manufacturefor adaptive passive scanning and/or adaptive active probing techniquesto support mobile device positioning.

2. Information

Mobile devices, such as mobile phones, notebook, computers, etc.,typically have the ability to estimate location and/or position with ahigh degree of precision using any one of several technologies such as,for example, satellite positioning systems (e.g., GPS and the like),advanced forward-link trilateration (AFLT), just to name a few examplesof signal-based positioning systems and/or corresponding signal-basedpositioning signals. Using high precision location information,applications for a mobile device may provide a user with variousservices, such as, for example, vehicle/pedestrian navigation,location-based searching, just to name a couple of examples. Here, highprecision signal-based location information (e.g., obtained from GPSand/or other signal-based positioning systems) may be processedaccording to a global coordinate system (e.g., latitude and longitude orearth-centered xyz coordinates). While such use of signal-based locationinformation referenced to a global coordinate system may be useful inproviding some services (e.g., outdoor vehicle navigation), suchsignal-based location information referenced to a global coordinatesystem may be impractical for other types of services such as indoorpedestrian navigation.

In certain indoor environments, such as office buildings, shoppingmalls, airports, stadiums, etc., certain example signal-basedpositioning techniques may make use of various terrestrial-basedwireless signal transmitting devices, e.g., wireless network serviceaccess transceivers, cellular network base stations, special-purposebeacon transmitters, etc., that transmit wireless signals which may beacquired by the mobile device and used for positioning purposes. Forexample, a mobile device may receive a signal-based positioning signalfrom a transmitter and based thereon determine a pseudorange between thetransmitter and receiver. Hence, for example, positioning may beprovided based on trilateration and/or other known signal-basedpositioning techniques.

In some implementations, an indoor navigation system may provide adigital electronic map to mobile devices as they enter a particularindoor area. Such an electronic map may show indoor features such asdoors, hallways, entry ways, walls, etc., points of interest such asbathrooms, pay phones, room names, stores, etc. Such an electronic mapmay be stored at a server to be accessible by a mobile device throughselection of a URL, for example. By obtaining and rendering all or partof an electronic map via a display mechanism, a mobile device may, forexample, overlay a current location of the mobile device (and user) overthe displayed map to provide the user with additional context.

In certain instances, in addition to an electronic map, an indoornavigation system may selectively provide assistance information tomobile devices to facilitate and/or enable various location basedservices. Such assistance information may include, for example,information to facilitate measurements of ranges to wireless serviceaccess transceivers at known fixed locations. In one implementation, Forexample, a “radio heatmap” or “probability heatmap” indicating and/orotherwise modeling expected RSSI and/or round-trip delay times atparticular locations associated with service access transceivers mayenable a mobile device to associate acquired signal measurements withone of the particular locations in an indoor environment. Here, forexample, grid points may be laid over locations in an indoor environmentat a uniform spacing (e.g., 0.5 meter separation of neighboring gridpoints), or possibly with non-uniform spacing. Thus, radio heatmapand/or other corresponding probability functions/models may be madeavailable from a computing device (such as a server) for each grid pointcovering an indoor environment.

SUMMARY

In accordance with certain aspects, a method may be provided whichcomprises, with a mobile device: acquiring signals from a plurality ofwireless transceivers; identifying each of the plurality of wirelesstransceivers based, at least in part, on one or more of the acquiredsignals; determining a received signal strength measurement for each ofthe plurality of wireless transceivers based, at least in part, on oneor more of the acquired signals; and determining a transmission power ofa probe signal to be transmitted to at least one of the plurality ofwireless transceivers based, at least in part, on at least one of thereceived signal strength measurements.

In accordance with certain other aspects, an apparatus may be providedfor use in a mobile device. Such an apparatus may, for example,comprise: means for acquiring signals from a plurality of wirelesstransceivers; means for identifying each of the plurality of wirelesstransceivers based, at least in part, on one or more of the acquiredsignals; means for determining a received signal strength measurementfor each of the plurality of wireless transceivers based, at least inpart, on one or more of the acquired signals; and means for determininga transmission power of a probe signal to be transmitted to at least oneof the plurality of wireless transceivers based, at least in part, on atleast one of the received signal strength measurements.

In accordance with still other aspects, a mobile device may be providedwhich comprises a processing unit to: identify each of a plurality ofwireless transceivers based, at least in part, on one or more signalsacquired from the plurality of wireless transceivers; determine areceived signal strength measurement for each of the plurality ofwireless transceivers based, at least in part, on one or more of thesignals acquired from the plurality of wireless transceivers; anddetermine a transmission power of a probe signal to be transmitted to atleast one of the plurality of wireless transceivers based, at least inpart, on at least one of the received signal strength measurements.

In accordance with still further aspects, an article of manufacture maybe provided for use by mobile device. For example, such an article ofmanufacture may comprise a non-transitory computer readable mediumhaving computer implementable instructions stored therein that areexecutable by a processing unit in the mobile device to: initiateacquisition of signals from a plurality of wireless transceivers;identify each of the plurality of wireless transceivers based, at leastin part, on one or more of the acquired signals; determine a receivedsignal strength measurement for each of the plurality of wirelesstransceivers based, at least in part, on one or more of the acquiredsignals; determine a transmission power of a probe signal to betransmitted to at least one of the plurality of wireless transceiversbased, at least in part, on at least one of the received signal strengthmeasurements.

BRIEF DESCRIPTION OF DRAWINGS

Non-limiting and non-exhaustive aspects are described with reference tothe following figures, wherein like reference numerals refer to likeparts throughout the various figures unless otherwise specified.

FIG. 1 is a schematic block diagram illustrating an example environmentthat includes representative electronic devices that may perform and/orotherwise support certain adaptive passive scanning and/or adaptiveactive probing techniques to support mobile device positioning, inaccordance with an example implementation.

FIG. 2 is a schematic block diagram illustrating an example environmentthat includes a mobile device and a plurality of wireless transceiversfor use in certain adaptive passive scanning and/or adaptive activeprobing techniques supporting mobile device positioning, in accordancewith an example implementation.

FIG. 3 is a schematic block diagram illustrating certain features of acomputing platform that may be provided in a mobile device, to performadaptive passive scanning and/or adaptive active probing in support ofmobile device positioning, in accordance with an example implementation.

FIG. 4 is a flow diagram illustrating an example process that may beimplemented in a mobile device, to perform adaptive passive scanningand/or adaptive active probing in support of mobile device positioning,in accordance with an example implementation.

DETAILED DESCRIPTION

Certain mobile device positioning techniques are based, at least inpart, on wireless signals transmitted between a mobile device and one ormore other devices (e.g., one or more wireless transceivers). Suchmobile device positioning techniques may be used to determine a locationof the mobile device relative to some coordinate system, map, graph,etc., determine a range from the mobile device to another device and/orobject, determine one or more parameters associated with movement of themobile device, and/or support navigation or other location basedservice(s) that may be provided, at least in part, through the mobiledevice, just to name a few examples. In certain instances, it may bebeneficial to select a subset of available wireless transceivers for usein such a mobile device positioning techniques since there may be aplethora of such wireless transceivers available in certainenvironments. Additionally, it may be beneficial to perform mobiledevice positioning quickly and/or efficiently, e.g., to improve a userexperience, prolong battery life, etc. Accordingly, various examplepassive scanning techniques are described herein which may be used toselect a subset of wireless transceivers. Further, in certain instances,a passive scanning technique may affect a transmit power setting or thelike, which may be used in a subsequently conducted active probingtechnique. For example, a transmit power of the mobile device may beaffected in some manner based, at least in part, on one or more receivedsignal strength measurements for wireless signals acquired by the mobiledevice during a passive scan. Thus, in certain instances a transmitpower of the mobile device may reduced from a maximum or nominalsetting, which may reduce power consumption. In other instances, atransmit power of the mobile device may be increased from a nominal orprevious setting, which may improve efficiency by increasing alikelihood that wireless signals subsequently transmitted by the mobiledevice may be acquired by the intended wireless transceivers. Hence,such passive scanning techniques may, for example, be referred to as“adaptive passive scanning” techniques.

With this in mind, various example implementations are described andillustrated herein by which certain adaptive passive scanning and activeprobing techniques may be realized to support mobile device positioning.As described herein certain passive scanning operations may be conductedby a mobile device to adapt a transmit power to a current environmentsurrounding the mobile device. As described herein certain activeprobing operations may be conducted based on such an adaptivelydetermined transmit power.

Further, as described herein certain active probing operations may beconducted by a mobile device to limit corresponding probe signaltransmissions to a selected subset of wireless transceivers within thecurrent environment. Accordingly, in certain instances, such adaptivetechniques, alone and/or combined with other techniques, may allow amobile device to determine (e.g., estimate) its location in a mannerwhich may reduce an amount of electrical power consumed, reduce anamount of time required to determine such a location, reduce a number ofwireless transmissions, lower processing resource usage, wirelesstransmitter device selection processes, and/or the like or somecombination thereof.

As described in greater detail by way of several exampleimplementations, various techniques are provided for use with a mobiledevice in calculating an estimated location of the mobile device basedon wireless signals acquired from one or more wireless transceivers(e.g., wireless service access transceivers, repeater devices, alocation Beacon devices, etc.).

For example, in certain implementations, a mobile device may receivewireless signals from a plurality of wireless transceivers as part of apassive scanning operation in which the mobile device may furtheridentify each of the plurality of wireless transceivers based, at leastin part, on information (e.g., a unique identifier, locationcoordinates, etc.) that may be encoded in one or more of the acquiredsignals. The mobile device may also associate a received signal strengthmeasurement with individual wireless transceivers. A mobile device maydetermine and/or otherwise affect a transmission power of a probe signalthat may be later transmitted by the mobile device to at least one ofthe wireless transceivers based, at least in part, on at least one ofthe received signal strength measurements.

In certain further example implementations, a mobile device may directprobe signals for transmission to a selected subset of wirelesstransceivers, e.g. as part of a subsequent active probing operation.Here, for example, mobile device may determine a transmission power foruse in transmitting such probe signals based, at least in part, on alowest received signal strength measurement for acquired wirelesssignals from among the selected subset of wireless transceivers. Asdescribed in greater detail herein, in certain example implementations,one or more wireless transceivers may be included in or possiblyexcluded from a subset of wireless transceivers based on certain otherfactors and/or considerations.

In certain example implementations, as part of an active probingoperation, a mobile device may use its communication interface totransmit, at a first time, a particular probe signal to a particularwireless transceiver that is in the subset of wireless transceivers. Ata second time that is subsequent to the first time, the mobile devicemay receive a response to the particular probe signal from theparticular wireless transceiver. The mobile device may, for example,compute a range to the particular wireless transceiver based, at leastin part, on the period of time between first time and the second time.In certain example implementations, mobile device may further computeits estimated location based, at least in part, on one or more computingranges to one or more wireless transceivers having known locations.Here, for example, in certain implementations, a range to a wirelesstransceiver may be based on a round trip time determined based, at leastin part, on the first time and the second time, e.g., minus an expectedprocessing time associated with a wireless transceiver.

In certain example implementations, to possibly improve accuracy inpositioning, in selecting a subset of wireless transceivers to receiveprobe signals, a mobile device may select certain available wirelesstransceivers in a manner that may increase the diversity of angulardirections from the mobile device to the wireless transceivers, andwhich may improve accuracy in positioning, e.g., based on trilateration,etc. Thus, in certain implementations if two wireless transceivers mayfall along a single line (angle) from an approximate location the mobiledevice, or have angles from the approximate location the mobile devicethat are determined to be too close together (e.g., based on a thresholdvalue), then it may be useful to select one, but not both, of thewireless transmitters for inclusion in a subset of wireless transmittersif possible. Thus, in certain implementations, a mobile device mayselect between two available wireless transceivers for inclusion orexclusion from a subset based, at least in part, on an angularseparation between the two wireless transceivers from a vantage point ofan approximate location of the mobile device. In certain exampleimplementations, an angular threshold value may be considered which maybe based, at least in part, on a dilution of precision (DOP) thresholdvalue relating to the positioning technique being performed or otherwisesupported by the mobile device. For example, an angular threshold valuemay be based, at least in part, on a threshold number of wirelesstransceivers to be included within a subset of wireless transceivers,and in certain implementations such a threshold number of wirelesstransceivers may be based, at least in part, on a DOP threshold value.

With this introduction mind, attention is drawn to FIG. 1, which is aschematic block diagram illustrating an example environment 100 thatincludes representative electronic devices that may perform and/orotherwise support certain adaptive passive scanning and/or adaptiveactive probing techniques to support mobile device positioning, inaccordance with an example implementation.

Example environment 100 comprises a mobile device 104 having anapparatus 110 capable of performing certain adaptive passive scanningand/or adaptive active probing techniques in accordance with certainexample implementations.

As used herein a “mobile device” may represent any electronic devicethat may be moved about either directly or indirectly by a user withinan indoor environment and which may communicate with one or more otherdevices via one or more wired and/or wireless communication links. Someexamples include a cell phone, a smart phone, a computer (e.g., apersonal computer such as a laptop computer, tablet computer, a wearablecomputer, etc.), a navigation aid, a tracking device, a digital bookreader, a gaming device, music and/or video player device, a camera, amachine, a robot, etc.

As illustrated in FIG. 1, at certain times mobile device 104 may belocated within an indoor environment 125. The indoor environment 125may, for example, represent one or more natural and/or man-madestructures forming a full or partial enclosure. In certainimplementations, such an indoor environment 125 may interfere withcertain wireless positioning signals, e.g., such as those transmittedfrom a satellite positioning systems.

As illustrated however, while located within indoor environment 125mobile device 104 may, for example, receive one or more wireless signalsfrom one or more terrestrial-based wireless transceivers 140 over one ormore wireless communication links 142. For example, mobile device 104may receive one or more wireless signals from one or more wirelesstransceivers 140 as part of a passive scanning operation, and/or as partof an active probing operation. Likewise, mobile device 104 may, forexample, transmit one or more wireless signals to one or more wirelesstransceivers 140 over one or more wireless communication links 142. Forexample, mobile device 104 may transmit one or more wireless signals toone or more wireless transceivers 140 as part of an active probingoperation.

As illustrated, wireless transceivers 140 may be provisioned within anindoor environment 125, or outside of indoor environment 125, or withinone or more network(s) 120, and configured to transmit and receive oneor more wireless signals over one or more wireless communication links142. Here, for example, such wireless signals may be used by mobiledevice 104 for positioning and/or navigation purposes.

As used herein, a “wireless transceiver” may represent any electronicdevice capable of transmitting and acquiring (e.g., receiving andunderstanding) one or more wireless signals in one or more wirelesscommunication links. Wireless signals transmitted by a wirelesstransmitter may be acquired by the mobile device for use in positioning.By way of example, in certain implementations a wireless transceiver 140may comprise a service access transceiver (e.g., an IEEE Standard 802.11access point device and/or other like electronic device that may be partof a wireless local area network and/or other like communicationcapability). Such a service access transceiver and/or other likeelectronic device may, for example, provide additional connectivity toone or more other wired and/or wireless networks. Such a service accesstransceiver and/or other like electronic device may, for example,provide direct and/or indirect connectivity (e.g., via one or morenetworks, etc.) to one or more other computing resources (devices) 130.Thus, for example, in certain implementations a wireless transceiver 140may provide mobile device 104 with access to additional communicationand/or computing resources. However, in certain other implementations,one or more wireless transceivers 140 may be provisioned to providelimited support to a mobile device, e.g., as part of a positioningand/or navigation capability. Here, for example, a wireless transceiver140 may take the form of a dedicated positioning resource, and/or thelike as part of a location based service within an indoor environment,etc. Thus, a mobile device may be limited to simply transmitting to andacquiring wireless signals from such a dedicated positioning resource,for use in positioning/navigation. Regardless of its form, a wirelesstransceiver 140 may be uniquely identified and as such identifiablebased, at least in part, on one or more wireless signals transmitted bythe wireless transceiver. For example, a wireless signal transmitted bya wireless transceiver may be indicative of a unique identifier, e.g., aMAC address, etc. Further, wireless transceiver 140 may be arranged totransmit wireless signals from, and receive wireless signals at, a knownlocation. In certain example implementations, a known location of awireless transceiver 140 may be determined based, at least in part, onone or more wireless signals transmitted by the wireless transceiver.For example, in certain instances a wireless transceiver 140 mayidentify all or part of its location in a wireless signal. Here, forexample, a wireless signal may comprise one or more coordinates and/orthe like that is indicative of a location of the transmitting device'santenna(s). In another example, a wireless signal may compriseadditional information (e.g., unique identifier, MAC address, etc.) thatmay be used to determine a known location of a wireless transceiver.Here, for example, one or more coordinates and/or the like that isindicative of a location of the transmitting device's antenna(s) may bedetermined via a database, lookup table, radio heatmap, probabilityheatmap, etc., based, at least in part, on unique identifier for thewireless transceiver. In certain example implementations, such adatabase, lookup table, etc., may be provisioned in the mobile device,e.g., as part of or in addition to an electronic map, etc. In certainexample implementations, such a database, lookup table, radio heatmap,probability heatmap, etc., may be provisioned in one or more otherdevices external to the mobile device, which may be contacted (e.g., viaa communication interface) to perform or otherwise support adetermination process that associates the additional informationacquired from a wireless transceiver with a known location of a wirelesstransceiver.

As illustrated, one or more satellite positioning system systems (SPS)150 may be provided to transmit one or more wireless positioning signalsin the form of one or more SPS signals 152 that may, at times, beacquired by mobile device and used for positioning and/or navigationpurposes.

Network(s) 120 may comprise one or more communication systems and/ordata networks having various interconnected devices supportingcommunication between computing device 102 and one or more otherresources (devices) 130. As mentioned, network(s) 120 may furthersupport communication between mobile device 104 and one or morecomputing resources (devices) 130. For example, communication betweenmobile device 104 and one or more computing resources (devices) 130 mayallow for certain data and/or instructions to be exchanged therebetween. In certain implementations, computing resources (devices) 130may also be used in similar fashion by one or more wireless transceivers140 and/or other like devices within networks 120.

Computing resources (devices) 130 may represent one or more computingplatforms from which mobile device 104 may obtain certain data filesand/or instructions, and/or to which mobile device 104 may providecertain data files and/or instructions. For example, in certaininstances, all or part of an electronic map, a connectivity map, aroutability graph, certain positioning and/or navigation assistancedata, and/or the like may be obtained by mobile device 104 from one ormore computing resources (devices) 130. For example, in certaininstances, all or part of a set of instructions for use in apparatus 110may be obtained from one or more computing resources (devices) 130.

As mentioned, SPS 150 which may transmit one or more SPS signals 152 tomobile device 104. SPS 150 may, for example, represent one or moreglobal navigation satellite system (GNSS), one or more regionalnavigation satellite systems, and/or the like or some combinationthereof. Additionally, one or more terrestrial-based positioning systemsmay be provided as represented by one or more wireless transceivers 140capable of transmitting one or more wireless signals all or some ofwhich may be used for signal-based positioning. Thus, for example, asmentioned one or more wireless transceivers 140 may represent a wirelessservice access transceiver, a base station, a repeater, a dedicatedbeacon transmitting device, just to name a few examples, which haveknown positions. SPS signals 152 and/or wireless signals obtained viawireless communication link(s) 142 may, at times, be acquired by mobiledevice 104 and used to calculate its estimated location, etc.

In certain implementations, mobile device 104 may receive or acquire SPSsignals 152 from SPS satellites (not shown). In some embodiments, SPSsatellites may be from one GNSS, such as the GPS or Galileo satellitesystems. In other embodiments, the SPS Satellites may be from multipleGNSS such as, but not limited to, GPS, Galileo, Glonass, or Beidou(Compass) satellite systems. In other embodiments, SPS satellites may befrom any one several regional navigation satellite systems (RNSS') suchas, for example, WAAS, EGNOS, QZSS, just to name a few examples.

In certain implementations, mobile device 104 may transmit wirelesssignals to, and receive wireless signals from, a wireless communicationnetwork (e.g., represented by network(s) 120). In one example, mobiledevice may communicate with a cellular communication network (e.g.,represented by network(s) 120) by transmitting/acquiring wirelesssignals 122 to/from a base station transceiver or the like.

In a particular example implementation, mobile device 104 and/orcomputing resources (devices) 130 may communicate with each other and/orother resources (devices) 130 over network(s) 120. As mentioned,network(s) 120 may comprise any combination of wired or wireless links.In a particular implementation, network(s) 120 may comprise an InternetProtocol (IP) infrastructure and/or the like, which may be capable offacilitating communication between mobile device 104 and/or computingresources (devices) 130. In another example implementation, network(s)120 may comprise cellular communication network infrastructure such as,for example, a base station controller or master switching center tofacilitate mobile cellular communication with at least mobile device104.

In particular implementations, and as discussed below, mobile device 104may have circuitry and processing resources capable of computing aposition fix (e.g. calculating an estimated location) of mobile device104. For example, mobile device 104 may compute a position fix based, atleast in part, on pseudorange measurements to one or more SPSsatellites. Here, mobile device 104 may compute such pseudorangemeasurements based, at least in part, on of pseudonoise code phasedetections in SPS signals 152 acquired from one or more SPS satellites.In particular implementations, mobile device 104 may receive SPSpositioning assistance data that may aid in the acquisition of SPSsignals 152 transmitted by SPS 150 including, for example, almanac,ephemeris data, Doppler search windows, just to name a few examples.

In other implementations, mobile device 104 may obtain a position fix byprocessing signals acquired from one or more cellular networktransmitting devices and/or the like having known positions (e.g., suchas base station transceiver, etc.) using any one of several techniquessuch as, for example, advanced forward trilateration (AFLT), observedtime difference of arrival (OTDOA), etc. In certain exampleimplementations, a range from mobile device 104 may be measured to aplurality of such cellular network transmitting devices, e.g., based, atleast in part, on pilot signals transmitted by the cellular networktransmitting devices from their known locations and acquired at mobiledevice 104. In certain instances, network(s) 120 and/or computingresources(devices) 130 may be capable of providing certain forms ofcellular network positioning assistance data to mobile device 104, whichmay include, for example, locations and identities of base transceiverstations, etc., to facilitate certain positioning techniques that mightuse cellular network signals. For example, a base station almanac (BSA)which indicates locations and identities of cellular base stations in aparticular region or regions.

In particular environments, such as indoor environment 125, mobiledevice 104 may not be capable of acquiring signals from a sufficientnumber of SPS satellites and/or from a sufficient number of cellularnetwork transmitting devices to effectively perform the requisiteprocessing to efficiently compute a position fix. However, mobile device104 may be capable of computing a position fix based, at least in part,on one or more wireless signals acquired from one or more wirelesstransceivers 140 (e.g., WLAN service access transceivers positioned atknown locations, etc.). For example, mobile device 104 may obtain aposition fix by measuring ranges to one or more indoor terrestrialwireless service access transceivers which may be positioned at knownlocations. Such ranges may be measured, for example, by obtaining a MACaddress and/or the like from signals acquired from such service accesstransceivers and obtaining range measurements to the service accesstransceivers by measuring one or more characteristics of one or moresignals acquired from such service access transceivers such as, forexample, received signal strength indicator (RSSI) or round trip time(RTT). In alternative implementations, mobile device 104 may obtain anindoor position fix by applying characteristics of acquired signals to aradio heatmap, probability heatmap, and/or the like or some combinationthereof indicating expected RSSI and/or RTT signatures at particularlocations in the indoor environment.

Terrestrial-based wireless positioning signal systems typically rely ondeployment of several wireless transceivers 140 (e.g., WiFi hotspots) atfixed(known) locations to enable a mobile device to obtain rangemeasurements to the fixed locations based, for example, on measurementsof signals transmitted from the wireless transceivers as pointed outabove. However, some indoor areas, e.g., such as representative indoorenvironment 125, may have an overly dense population of wirelesstransceivers, and as such, it may be beneficial to make use of just afew selected wireless transceivers.

Thus, in accordance with certain aspects of the present description,some example passive scanning operations and active probing operationsare presented which may be adapted to particular situations,environments, devices, needs, etc. In one example, a passive scanningoperation may be implemented in a mobile device to select certainwireless transceivers for use in positioning. In one example, passivescanning operation may be implemented in a mobile device to determine atransmit power for use in a subsequent active probing operation. In oneexample, an active probing operation may be implemented in a mobiledevice to probe selected wireless transceivers, e.g., as determined aspart of a passive scanning operation. In one example, an active probingoperation may be implemented in a mobile device to probe selectedwireless transceivers based on an adapted transmit power, e.g., asdetermined as part of a passive scanning operation.

With this in mind, reference is made next to FIG. 2, which is aschematic block diagram illustrating an example environment 200 thatincludes mobile device 104 and a plurality of wireless transceivers foruse in certain adaptive passive scanning and/or adaptive active probingtechniques supporting mobile device positioning, in accordance with anexample implementation.

More specifically, in this example, mobile device 104 is illustrated asbeing arranged in an environment 200 amongst a plurality of wirelesstransceivers 140-1 through 140-8. In this example, it is assumed thateach of the illustrated wireless transceivers shares a few traits.

The first shared trait is that a wireless transceiver may, from time totime, transmit (e.g., operating in a broadcasting or other like mode)one or more wireless signals that may be acquired by mobile device 104.By acquiring such wireless signal(s), a mobile device 104 may identifythe transmitting wireless transceiver and measure a received signalstrength. By way of an example, wireless transceivers 140-1 through140-8 may each transmit one or more beacon signals and/or the like thatmay be properly acquired by mobile device 104 under certain conditions(e.g., the transmitted wireless signal arrives at the mobile device in acondition that allows the mobile device to recover applicableinformation carried by the transmitted wireless signal). In certainexample implementations, the acquisition of such wireless signals may bereferred to as “passive scanning” or other similar terms because mobiledevice 104 may receive such wireless signals without activelytransmitting any particular signals. Hence, mobile device 104 may, fromtime to time, “passively scan” for wireless signals from one or morewireless transceivers. Such a passive scan may identify one or morenearby wireless transceivers and obtain respective received signalstrength measurements.

A wireless transceiver may be identified, for example, by one or morenumbers, character strings, bit strings, etc., that may be considered tobe substantially unique either universally and/or within certaincontexts. For example, as mentioned, certain devices may be identifiedbased on an assigned media access control (MAC) address, etc.

A received signal strength measurement may, for example, comprise somevalue or other like indication that is based, at least in part on apower level of a wireless signal as acquired by mobile device 104. Sucha received signal strength measurement may, for example, be based, atleast in part, on a maximum magnitude, a minimum magnitude, an averagemagnitude, an instantaneous or otherwise sampled magnitude, and/or someother measurable power related value for an acquired wireless signal.

In certain instances, mobile device 104 may further determine a locationof a wireless transceiver identified during a passive scan. For example,in certain instances, a beacon or other like signal may be indicative ofa location of its wireless transceiver. For example, in certaininstances, a mobile device may use other information (e.g., positioningand/or navigation assistance data, etc.) to obtain a location of anidentified wireless transceiver. A location of a wireless transceivermay, for example, indicate certain applicable coordinates for thewireless transceiver with regard to a particular coordinate system.

A trait that may be shared by certain wireless transceivers may be, thatunder certain conditions, a probe signal transmitted by mobile device104 at a first time may be acquired, and in response, at a later time(subsequent to the first time) a response signal may be transmitted backto mobile device 104 and which may be acquired by the mobile device at asecond time. Such active exchange of signals may, for example, beperformed according to a process in which the wireless transceiverensures that a particular period of time (e.g., an expected processingperiod) passes from the time that the probe signal is acquired by thewireless transceiver until the response signal it transmitted.Accordingly, mobile device 104 may determine at least a round trip time(RTT) based, at least in part, by subtracting the expected processingperiod from the period of time between the first time and the secondtime. In certain implementations, other like time measurements may bedetermined using other known techniques. For example, if the mobiledevice and the wireless transceiver are synchronized or their clockoffsets are known it may be possible to determine a time of flight foreither a probe signal or a response signal. Moreover, a range betweenthe respective antennas of the mobile device and the wirelesstransceiver may be determined based, at least in part, on the RTT orother like time measurement(s), e.g., based, at least in part, on anexpected wireless signal propagation speed.

In certain example implementations, mobile device 104 may determinefurther identifying information (e.g., a unique identifier, a MACaddress, etc.) for a wireless transceiver based, at least in part, on apassive scan. For example, in certain instances, a beacon or other likesignal may be indicative of some operative characteristic of thetransmitting wireless transceiver, e.g., a type of the wirelesstransceiver, a capability of the wireless transceiver, a networkaffiliation of the wireless transceiver, etc. For example, in certaininstances, a mobile device may use other information (e.g., positioningand/or navigation assistance data, etc.) to obtain information relatingto such operative characteristics. In certain example implementations, awireless transceiver may be selected for subsequent active probingand/or other purposes by mobile device 104 based, at least in part, onone or more of its operative characteristics. For example, one or morewireless transceivers may be selected as part of a subset of wirelesstransceivers for active probing based, at least in part, on the type ofdevice that the wireless transceiver may be part of her operativelyassociated with. Here, for example, it may be beneficial to select asubset of wireless transceivers that are part of a particular locationbased system, network, etc. Hence, for example, a subset of wirelesstransceivers may comprise service access transceivers and/or the likethat may be operatively provided as part of a wireless local areanetwork.

In another example one or more wireless transceivers may be selectedbased on the one or more operative characteristics indicating that thewireless transceiver may support additional operations that may beundertaken by a mobile device. For example, a wireless transceiver maybe selected as part of the subset of wireless transceivers based, atleast in part, on an operative characteristic such as providing locationbased services, electronic maps, etc., which may be associated with aparticular indoor environment. In yet another example, a wirelesstransceiver may be selected based at least in part on an operativecharacteristic identifying and/or otherwise likely indicating that itadheres to and/or otherwise satisfy certain desired security procedures,e.g., with regard to safeguarding private information, locationinformation, and/or the like which may be associated with a mobiledevice and/or its user. Thus, a few examples have been provided above toillustrate that in addition to selecting a subset of wirelesstransceivers for active probing based, at least in part, on theirreceived signal strengths obtain during passive scanning, in certaininstances one or more of the wireless transceivers may be selected foradditional reasons, such as one or more operative characteristics thatmay be identified.

With such shared traits in mind, as illustrated in FIG. 2, with mobiledevice 104 operating in a passive scan mode, wireless signals (e.g.,beacon signals, etc.) may be acquired from wireless transceivers 140-1through 140-7, but not 140-8. Here, for example, wireless transceiver140-8 is represented as being too far away from mobile device 104 and/oras passively having its wireless signal interfered with too much topermit mobile device 104 from acquiring the wireless signal transmittedby wireless transceiver 140-8.

Thus, in this example, it will be assumed that as a result of at leastone passive scan, mobile device 104 has acquired wireless signals fromwireless transceivers 140-1 through 140-7. Accordingly, mobile device104 may be capable of uniquely identifying each of wireless transceivers140-1 through 140-7 and possibly transmitting corresponding probesignals to one or more of wireless transceivers 140-1 through 140-7.Moreover as previously described, mobile device 104 may also compriseknowledge as to the location for each of wireless transceivers 140-1through 140-7. Further still, as previously described mobile device 104may also comprise a received signal strength measurement for each ofwireless transceivers 140-1 through 140-7.

Although not drawn to scale, FIG. 2 is intended to illustrate that theremay be different ranges between mobile device 104 and each of wirelesstransceivers 140-1 through 140-7. For example, wireless transceivers140-1, 140-2, 140-3, and 140-4 appear to be somewhat closer to mobiledevice 104 then wireless transceivers 140-5, 140-6 and 140-7. Of courseit should be recognized that in certain instances, different wirelesstransceivers may transmit their respective wireless signals at differentpower levels. Additionally, should be recognized that in certaininstances, wireless transceivers may have different antenna designsand/or other like arrangements, and/or coverage areas, which in additionto distance may affect a received signal strength at mobile device 104.Further, as illustrated by object 206 which affects the wireless signalfrom wireless transceiver 140-4, one or more objects and/or otherwiseintervening materials may affect a received signal strength and/or othercharacteristics of the wireless signal after transmission. Nonetheless,one of the characteristics of acquired wireless signals that may becompared following a passive scanning operation are the respectivereceived signal strength measurements. Indeed, in certain instances, itmay be that the wireless signals with the relatively higher receivedsignal strengths correspond to wireless transceivers that may be closerto mobile device 104 then other wireless transceivers. Thus, forexample, a wireless signal acquired from wireless transceiver 140-1 mayhave a higher received signal strength measurement then it wirelesssignal acquired from wireless transceiver 140-7 do, at least in part towireless transceiver 140-1 being much closer to mobile device 104 thenwireless transceiver 140-7.

As illustrated, by a the dashed line 210, a range between mobile device104 and wireless transceiver 140-2 may be determined based, at least inpart, on a round trip time and/or other like a propagation timingmeasurement that may be observed and measured during an active probingoperation.

As described in greater detail herein, mobile device 104 may determine atransmission power for use in the transmitting a probe signal to asubset of wireless transceivers based, at least in part, on at least oneof the received signal strengths measured as part of the passive scanoperation. With this in mind, in transmitting a particular probe signalto a particular wireless transceiver, mobile device 104 may exhibit aparticular coverage area that may be based, at least in part, thedetermined transmission power. Thus, for example, FIG. 2 includes acoverage area 208 which, in this example extends outwardly in an omnidirectional manner from an antenna(s) of mobile device 104 with anexample radius 212. It should be understood that this is just asimplified drawing and then to an actual coverage area may be much morecomplex. Further, it should be understood that different wirelesstransceivers may be more or less sensitive in acquiring wireless signalsfrom mobile device 104. Further still, it should be understood that raceobjects and/or other materials may be arranged between a mobile device104 and a wireless transceiver, which may affect the transmitted signalin some manner.

However, even with this in mind, in accordance with certainimplementations, it may be beneficial to determine a transmission powerfor use in transmitting one or more probe signals to one or morewireless transceivers based, at least in part, on at least one of thereceived signal strengths measured as part of the passive scanoperation. For example, in certain implementations, a subset of wirelesstransceivers may be selected based, at least in part, on theirrespective received signal strengths measured during a passive scan. Thenumber of wireless transceivers in a subset may, for example, varydepending upon various factors, including, for example, a desired levelof accuracy in determining an estimated location of the mobile device, anumber of probe signals that may need to be transmitted, one or moreprocessing resource considerations, a power usage consideration, etc. Incertain example implementations, one or more threshold values may bepredetermined and/or dynamically determined based on one or more ofthese and/or other like considerations.

Indeed, by way of one example, a desired number of wireless transceiversto be included in a subset of wireless transceivers, and/or theinclusion or exclusion of one or more particular wireless transceiverswith regard to such a subset of wireless transceivers may be determinedbased, at least in part, on a dilution of precision (DOP) and/or thelike. Thus, for example, consider the illustrated locations of wirelesstransceivers 140-5 and 140-6 with regard to mobile device 104. Asillustrated there is a slight offset illustrated by an angle 203 betweena directional line 202 from mobile device 104 to wireless transceiver140-5 and another directional line 204 from mobile device 104 towireless transceiver 140-6. Here, in this example, it may be assumedthat the angle 203 may represent several degrees, or perhaps a fractionof one degree, and/or in certain instances zero degrees (0°). Hence, incertain instances wireless transceivers 140-5 and 140-6 may be locatedin about the same direction with the same or different distances, or maybe located at different distances along the same line extending frommobile device 104. Accordingly, it may be less useful to use wirelesstransceivers 140-5 and 140-6 for positioning and/or other likenavigation functions since their locations may not be as angularlyseparated as might other wireless transceivers. Hence for example, adesired DOP may not be met by a subset of wireless transceivers havingtoo few numbers of wireless transceivers and/or too few wirelesstransceivers having at least a threshold level of angular separation.Thus, in certain example implementations it may be beneficial to ofwireless transceivers 140-5 or 140-6 for inclusion in a subset ofwireless transceivers, e.g., and assuming there are enough otheravailable wireless transceivers for selection.

As described herein, by actively probing each of the wirelesstransceivers in such a subset of wireless transceivers in determining around trip time and/or other like propagation timing measurements,ranges may be calculated between mobile device 104 and each of theactively probe wireless transceivers. With this in mind, in certainexample implementations, a subset of wireless transceivers may comprisetwo or more wireless transceivers. In certain instances, an estimatedlocation of a mobile device may be improved by increasing the number ofwireless transceivers included in a subset of wireless transceivers, andhence the number of ranges available. Thus, for example, in certainimplementations a rough estimate of a location of a mobile device may beobtained using two different ranges, and a more accurate location may beobtained using three different ranges, and an even more accuratelocation may be obtained using four or more different ranges.

Hence, it maybe useful to balance the number of wireless transceivers tobe actively probe based on a desired accuracy of an estimated locationof the mobile device. In accordance with certain aspects, a subset ofwireless transceivers may be determined based, at least in part,selecting wireless transceivers whose received signal strengthmeasurements are less than or equal to a selected received signalstrength measurement used to determine a transmission power for use insubsequently transmitting probe signals. For example, in certainimplementations, a plurality of wireless transceivers identified duringa passive scan operation may be (at least logically) ordered based ontheir received signal strength measurements, e.g., in a descending orderfrom a highest received signal strength measurement to a lowest receivedsignal strength measurement. Hence, for example, if K represents athreshold number of wireless transceivers to be used in estimating alocation of a mobile device, then and a top-K number of wirelesstransceivers may be selected from such an ordered set starting from thewireless transceiver having highest received signal strengthmeasurement.

By way of example, let us assume that the received signal strengthmeasurements in TABLE 1 below were obtained by mobile device 104:

TABLE 1 Received Signal Strength Wireless Transceiver Measurement (seeFIG. 2) (relative nominal values) 140-1 1.00 140-2 0.92 140-3 0.83 140-40.51 140-5 0.74 140-6 0.63 140-7 0.46

Although the received signal strength measurements are illustratedherein using relative nominal values for simplification purposes, itshould be understood that in certain example implementations, a receivedsignal strength measurement may represent a particular unit ofmeasurement, and/or that such units of measurement may apply to a scalethat linear, logarithmic, etc.

With this in mind, as can be seen, if K equals 2 then a subset ofwireless transceivers may comprise wireless transceivers 140-1 and140-2. Moreover, a transmit power for subsequent active probing may bedetermined based, at least in part, on the lowest received signalstrength from the subset, which in this instance would be 0.92 fourwireless transceiver 140-2. In another example, if K equals 3 then asubset of wireless transceivers may comprise wireless transceivers140-1, 140-2 and 140-3; and/or a transmit power for subsequent activeprobing may be determined based, at least in part, on the lowestreceived signal strength from such a subset, which in this instancewould be 0.83 for wireless transceiver 140-3. In yet another example, ifK equals 4 then a subset of wireless transceivers may comprise wirelesstransceivers 140-1, 140-2, 140-3, and 140-5; and/or a transmit power forsubsequent active probing may be determined based, at least in part, onthe lowest received signal strength from such a subset, which in thisinstance would be 0.74 for wireless transceiver 140-5.

As mentioned, in certain instances a subset of wireless transceivers maybe further intelligently selected based on various operatingcharacteristics that may be identified and/or taking into accountcertain angular separations. Thus, for example, let us assume that theremay be a preference based, least in part, on one or more operativecharacteristics to not use wireless transceivers 140-3 or 140-4. Forexample, wireless transceivers 140-3 and 140-4 may not have trustworthylocation information, may not support or otherwise properly adhere tocertain probing and/or security agreements, etc., and, if possible,mobile device 104 may seek to use other wireless transceivers. As such,if K equals 3 then a subset of wireless transceivers (that avoidswireless transceivers 140-3 and 140-4) may comprise wirelesstransceivers 140-1, 140-2 and 140-5; and/or a transmit power forsubsequent active probing may be determined based, at least in part, onthe lowest received signal strength measurement from such a subset,which in this instance would be 0.74 for wireless transceiver 140-5.Similarly, if K equals 4 then a subset of wireless transceivers (thatavoids wireless transceivers 140-3 and 140-4) may comprise wirelesstransceivers 140-1, 140-2, 140-5 and 140-6; and/or a transmit power forsubsequent active probing may be determined based, at least in part, onthe lowest received signal strength from such a subset, which in thisinstance would be 0.63 for wireless transceiver 140-6. However, aspreviously mentioned, in certain instances an angular separation betweenwireless transceivers 140-5 and 140-6 may not meet an angular separationthreshold. Thus, in certain instances, if K equals 4 then a subset ofwireless transceivers (that avoids wireless transceivers 140-3 and140-4, and takes into consideration an angular separation threshold) maycomprise wireless transceivers 140-1, 140-2, 140-5 or 140-6, and 140-7;and/or a transmit power for subsequent active probing may be determinedbased, at least in part, on the lowest received signal strength fromsuch a subset, which in this instance would be 0.46 for wirelesstransceiver 140-6.

As may be appreciated, power usage by mobile device 104 may be reducedat times by subsequently using a transmit power that may beintelligently determined based, at least in part, on a lowest or minimumreceived signal strength measurement for the wireless transceiverswithin a particular subset of wireless transceivers to be activelyprobed. Those skilled in the art will understand that various functionsand/or other like algorithms may be implemented to determine a transmitpower based, at least in part, on a received signal strength measurementobtained during a passive scan operation.

By way of a further example, in certain implementations a transmit powerfor the mobile device may be selected which is proportional with regardto its operative scale based, at least in part, on how proportional areceived signal strength measurement is to its own operative scale(e.g., an expected range of signal strengths from such wirelesstransceiver). In other words, for example, if a received signal strengthmeasurement appears to represent about 60% of an expected range ofsignal strengths for a given wireless transceiver, in certain instancesa transmit power for the mobile device may be adapted to represent about60% of a range of available transmit powers. In certain exampleimplementations, a received signal strength measurement and a transmitpower a share a common unit of measure and/or possibly even a similarscale.

Reference is made next to FIG. 3, which is a schematic block diagramillustrating certain features of a computing platform 300 that may beprovided in mobile device 104, to perform adaptive passive scanningand/or adaptive active probing in support of mobile device positioning,in accordance with an example implementation.

As illustrated computing platform 300 may comprise one or moreprocessing units 302 to perform data processing (e.g., in accordancewith the techniques provided herein, and/or apparatus 110, etc.) coupledto memory 304 via one or more connections 306. Processing unit(s) 302may, for example, be implemented in hardware or a combination ofhardware and software. Processing unit(s) 302 may be representative ofone or more circuits configurable to perform at least a portion of adata computing procedure or process. By way of example but notlimitation, a processing unit may include one or more processors,controllers, microprocessors, microcontrollers, application specificintegrated circuits, digital signal processors, programmable logicdevices, field programmable gate arrays, or the like, or any combinationthereof.

Memory 304 may be representative of any data storage mechanism. Memory304 may include, for example, a primary memory 304-1 and/or a secondarymemory 304-2. Primary memory 304-1 may comprise, for example, a randomaccess memory, read only memory, etc. While illustrated in this exampleas being separate from the processing units, it should be understoodthat all or part of a primary memory may be provided within or otherwiseco-located/coupled with processing unit(s) 302, or other like circuitrywithin mobile device 104. Secondary memory 304-2 may comprise, forexample, the same or similar type of memory as primary memory and/or oneor more data storage devices or systems, such as, for example, a diskdrive, an optical disc drive, a tape drive, a solid motion state memorydrive, etc

In certain implementations, secondary memory may be operativelyreceptive of, or otherwise configurable to couple to, a non-transitorycomputer readable medium 370. Memory 304 and/or non-transitory computerreadable medium 370 may comprise instructions 372 for use in performingdata processing, e.g., in accordance with the techniques and/or exampleapparatus 110 (FIG. 1) and/or all or part of one or more example process400 (FIG. 4), as provided herein.

Computing platform 300 may, for example, further comprise one or morecommunication interface(s) 308. Communication interface(s) 308 may, forexample, comprise one or more radios, represented here by one or morereceivers 310 and one or more transmitters 312. It should be understoodthat in certain implementations, communication interface 308 maycomprise one or more transceivers, and/or the like. Further, it shouldbe understood that although not shown, communication interface 308 maycomprise one or more antennas and/or other circuitry as may beapplicable given the radios function/capability.

By way of further example, communication interface(s) 308 may, forexample, provide connectivity to network(s) 120, one or more wirelesstransceivers 140, and/or one or more computing resources (devices) 130(FIG. 1), e.g., via one or more wired and/or wireless communicationlinks. Communication interface(s) 308 may implement one or morecommunication protocols as may be required to support one or more wiredand/or wireless communication links.

In certain example instances, mobile device 104 may comprise an SPSreceiver 318 capable of acquiring and processing SPS signals 152 insupport of one or more signal-based positioning capabilities.

In accordance with certain example implementations, communicationinterface(s) 308, one or more wireless transceivers 140, and/orcomputing resources in network(s) 120 may, for example, be enabled foruse with various wireless communication networks such as a wireless widearea network (WWAN), a wireless local area network (WLAN), a wirelesspersonal area network (WPAN), and so on. The term “network” and “system”may be used interchangeably herein. A WWAN may be a Code DivisionMultiple Access (CDMA) network, a Time Division Multiple Access (TDMA)network, a Frequency Division Multiple Access (FDMA) network, anOrthogonal Frequency Division Multiple Access (OFDMA) network, aSingle-Carrier Frequency Division Multiple Access (SC-FDMA) network, andso on. A CDMA network may implement one or more radio accesstechnologies (RATs) such as cdma2000, Wideband-CDMA (W-CDMA), TimeDivision Synchronous Code Division Multiple Access (TD-SCDMA), to namejust a few radio technologies. Here, cdma2000 may include technologiesimplemented according to IS-95, IS-2000, and IS-856 standards. A TDMAnetwork may implement Global System for Mobile Communications (GSM),Digital Advanced Mobile Phone System (D-AMPS), or some other RAT. GSMand W-CDMA are described in documents from a consortium named “3rdGeneration Partnership Project” (3GPP). Cdma2000 is described indocuments from a consortium named “3rd Generation Partnership Project 2”(3GPP2). 3GPP and 3GPP2 documents are publicly available. A WLAN mayinclude an IEEE 802.11x network, and a WPAN may include a Bluetoothnetwork, an IEEE 802.15x, for example. Wireless communication networksmay include so-called next generation technologies (e.g., “4G”), suchas, for example, Long Term Evolution (LTE), Advanced LTE, WiMAX, UltraMobile Broadband (UMB), and/or the like. Additionally, communicationinterface(s) 208 and/or communication interface(s) 308 may furtherprovide for infrared-based communications with one or more otherdevices. A WLAN may, for example, comprise an IEEE 802.11x network, anda WPAN may comprise a Bluetooth network, an IEEE 802.15x, for example.Wireless communication implementations described herein may also be usedin connection with any combination of WWAN, WLAN or WPAN. In anotheraspect, a wireless transmitting device may comprise a femtocell,utilized to extend cellular telephone service into a business or home.In such an implementation, one or more mobile devices may communicatewith a femtocell via a CDMA cellular communication protocol, forexample, and the femtocell may provide the mobile device access to alarger cellular telecommunication network by way of another broadbandnetwork such as the Internet.

Mobile device 104 may, for example, further comprise one or moreinput/output units 314. Input/output units 314 may represent one or moredevices or other like mechanisms that may be used to obtain inputs fromand/or provide outputs to one or more other devices and/or a user ofmobile device 104. Thus, for example, input/output units 314 maycomprise various buttons, switches, a touch pad, a trackball, ajoystick, a touch screen, a microphone, a camera, and/or the like, whichmay be used to receive one or more user inputs. In certain instances,input/output units 314 may comprise various devices that may be used inproducing a visual output, an audible output, and/or a tactile outputfor a user. For example, input/output units 314 may be used to present asolicitation to the user and to obtain certain corresponding userinputs.

Mobile device 104 may, for example, comprise one or more sensors 316.For example, sensor(s) 316 may represent one or more inertial sensors,one or more environmental sensors, etc., which may be useful indetecting aspects of the environment 100 and/or mobile device 104. Thusfor example, sensor(s) 316 may comprise one or more accelerometers, oneor one or more gyroscopes or gyrometers, one or more magnetometersand/or the like, one or more barometers, one or more thermometers, etc.Further, in certain instances sensor(s) 316 may comprise one or moreinput devices such as a microphone, a camera, a light sensor, etc.

In certain example implementations, one or more sensors 316 may be usedto detect and/or otherwise trigger an event which may initiate one ormore operations, such as, for example, a passive scanning operation, anactive probing operation, etc., e.g., as part of a positioning and/orother like navigation capability. Here, for example, the presence and/orabsence of certain signals from one or more inertial sensors may beindicative of a presence or absence of movements of mobile device 104.Thus, for example, it may be beneficial at certain times to initiate orotherwise affect a passive scanning operation and/or an active probingoperation in response to certain detected movements of mobile device104.

Processing unit(s) 302 and/or instructions 372 may, for example, provideor otherwise make use of one or more signals that may be stored inmemory 304 from time to time and which may represent data and/orinstructions, such as: instructions 372; apparatus 110; one or morewireless signals 320; one or more received signal strength measurements322; a transmit power 324; one or more times 326 (e.g., a first-timecorresponding to transmitting a probe signal, a second timecorresponding to acquiring a response signal, certain time periods,timestamps, local time, universal time, a time offset, etc.); one ormore probe signals 328; one or more responses 330 (e.g., acquired fromone or more wireless transceivers in response to one or more probesignals 328); one or more ranges 332 (e.g., between an antenna of themobile device and an antenna of a wireless transceiver); one or morelocations 334 (e.g., coordinates for one or more estimated locations ofthe mobile device, coordinates for known locations of one or morewireless transceivers, etc.); one or more threshold values 336;assistance data 340 (e.g., positioning assistance data, navigationassistance data, etc.); and/or the like or some combination thereof. Itshould be kept in line, that in certain example implementations, sometypes of data may comprise or otherwise be represented at least in partby one or more functions and/or other like computer implementableinstructions, e.g., which may be used to calculate certain data values,etc. Additionally, while some the example data and/or instructions asillustrated in FIG. 3 share the same reference numbers as example dataand/or instructions as illustrated in FIG. 2, it should be kept in mindthat in certain instances all or part of such example data and/orinstructions may be distinctly different.

SPS receiver 318 may be capable of acquiring and acquiring SPS signals152 via one or more antennas (not shown). SPS receiver 318 may alsoprocess, in whole or in part, acquired SPS signals 152 for estimating aposition or location of mobile device 104. In certain instances, SPSreceiver 318 may comprise one or more processing unit(s) (not shown),e.g., one or more general purpose processors, one or more digital signalprocessors DSP(s), one or more specialized processors that may also beutilized to process acquired SPS signals, in whole or in part, and/orcalculate an estimated location of mobile device 104. In certainimplementations, all or part of such processing of acquired SPS signalsmay be performed by other processing capabilities in mobile device 104,e.g., processing unit(s) 302, memory 304, etc., in conjunction with SPSreceiver 318. Storage of SPS or other signals for use in performingpositioning operations may be performed in memory 304 or registers (notshown).

Sensors 316 may generate analog or digital signals that may be stored inmemory 304 and processed by DPS(s) (not shown) or processing unit(s) 302in support of one or more applications such as, for example,applications directed to positioning or navigation operations.

Processing unit(s) 302 may comprise a dedicated modem processor or thelike that may be capable of performing baseband processing of signalsacquired and downconverted at receiver(s) 310 of communicationinterface(s) 308 or SPS receiver 318. Similarly, a modem processor orthe like may perform baseband processing of signals to be upconvertedfor transmission by wireless transmitter(s) 312. In alternativeimplementations, instead of having a dedicated modem processor, basebandprocessing may be performed by a general purpose processor or DSP (e.g.,general purpose/application processor). It should be understood,however, that these are merely examples of structures that may performbaseband processing, and that claimed subject matter is not limited inthis respect.

Reference is made next to FIG. 4, which is a flow diagram illustratingan example process 400 that may be implemented in mobile device 104and/or apparatus 110 (FIG. 1), to perform adaptive passive scanningand/or adaptive active probing in support of mobile device positioning,in accordance with an example implementation

At example block 402, one or more wireless signals may be acquired by awireless device from one or more wireless transceivers. As previouslymentioned, in certain instances, a wireless device may perform passivescanning operation in which one or more wireless signals may be acquiredfrom one or more wireless transceivers. In certain exampleimplementations, one wireless signal may comprise a Beacon signal and/orother like wireless signal that may be broadcast by the wirelesstransceiver from time to time. By way of one example, a wirelesstransceiver may take the form of a service access transceiver and/or thelike, which may be provided as part of a wireless local area networkand/or some other communication network(s). Such a service accesstransceiver may, for example, broadcast one or more messages whichidentify certain aspects about the service access transceiver to otherdevices that may be within the coverage area of the service accesstransceiver, such as a mobile device. As previously mentioned, and aswell known, such Beacon signals and/or other like wireless signals maycomprise and/or otherwise identifying some manner the transmittingdevice. Thus, for example, a service access transceiver and/or otherlike wireless transceiver may transmit its assigned unique identifier,such as a MAC address, a service set identifier (SSID), a uniformresource locator (URL), etc. Additionally, in certain implementations,certain wireless signals may also provide additional information aboutthe wireless transceiver. For example, certain wireless signals mayidentify coordinates for a location of the wireless transceiver. Forexample, certain wireless signals may identify certain operativecharacteristics of the wireless transceiver.

At example block 404, a mobile device may identify a particular wirelesstransceiver is having transmitted wireless signal has acquired at block402. At block 404, mobile device may further determine a correspondingreceived signal strength measurement for one or more wireless signalsacquired at block 402. As mentioned, a received signal strengthmeasurement may take on various forms, units, scales, etc., e.g.,depending upon the underlying design and/or use thereof within themobile device. In certain example implementations, a received signalstrength measurement may comprise a received signal strength indication(RSSI), and/or the like, associated with the measurement of the powerpresent in the acquired radio signal.

At example block 406, the mobile device may determine a transmissionpower of one or more probe signals to be transmitted to one or morewireless transceivers in a subset of wireless transceivers. Here, forexample, a transmission power may be based, at least in part, on atleast one received signal strength measurement. Thus, for example, aspart of block 406, a subset of wireless transceivers may be determinedbased, at least in part, on at least one of the received signal strengthmeasurements. Additionally, as previously mentioned, certain wirelesstransceivers may be selected for such a subset of wireless transceiversbased on one or more threshold values. For example, one threshold valuemay specify a subset of wireless transceivers is to comprise aparticular number of wireless transceivers, and/or at least a minimumnumber of wireless transceivers. For example, one threshold may specifythat certain wireless transceivers may be selected over other wirelesstransceivers for various reasons, including, for example, certainoperable characteristics of one or more of the wireless transceivers, anangular separation between certain wireless transceivers, etc.

At example block 408, as part of an example active probing operation, amobile device may transmit a probe signal (e.g., one or more messages)to a particular wireless transceiver within the subset of wirelesstransceivers from block 406. Indeed, as part of example block 408, amobile device may transmit an applicable probe signal to each of thewireless transceivers within the subset of wireless transceivers. Thus,for example, if there are four wireless transceivers within a subset ofwireless transceivers, then at example block 408, a mobile device maytransmit for separate probe signals, e.g., one probe signal for eachwireless transceiver. The probe signals may be transmitted by the mobiledevice using the transmission power as determined at example block 406.For a given probe signal and a given wireless transceiver, the mobiledevice may transmit the probe signal at a first time, and receive aresponse signal (e.g., one or more messages) to such a probe signal fromthe applicable wireless transceiver at a second time that is subsequentto the first time. Hence, for example, a round trip time associated withsuch active probing operation may be determined by subtracting a knownprocessing period consumed by the wireless transceiver from the periodof time between the first time and the second time. Here, such a roundtrip time may represent at least the combined propagation time for theprobe signal to travel from the antenna of the mobile device to theantenna of the wireless transceiver, and the propagation time for theresponse signal to travel from the antenna of the wireless transceiverto the antenna of the mobile device. In accordance with certain exampleimplementations, such an active probing operation may comprise the useof a request to send (RTS) (e.g., as a probe signal) and clear to send(CTS) (e.g., as a response signal) signaling/messaging techniques asprovided by IEEE 802.11 networking protocols, and/or the like.

At example block 410, a range from the mobile device to a wirelesstransceiver may be computed based, at least in part, on the first andsecond times. Here, for example, a point-to-point range between themobile device and such wireless transceiver may be determined based onan assumed speed of the propagating signal. Such ranging techniques andlike others are well known.

At example block 412, an estimated location of the mobile device may becomputed based, at least in part, on one or more of the ranges computedat block 410. Here, for example, trilateration and/or otherpositioning/navigation techniques may be implemented based on the rangesto and known locations of the wireless transceivers in the subset ofwireless transceivers previously selected. Such location estimationtechniques and like others are also well known. As part of block 412, incertain implementations, an estimated location of the mobile device maybe presented and/or otherwise indicated to a user of the mobile device,and/or shared with one or more other functions and/or processesperformed in a poor part on board the mobile device, and/or at one ormore other computing resources (devices). For example, in certainimplementations, an estimated location may be provided to a locationbased service entity, emergency responder, another mobile device, etc.

Example process 400, or particular portions thereof, may be repeatedfrom time to time, e.g., in response to a scheduled event, an occurrenceof some detectable event, a user input, an acquired wireless signal,etc. As previously mentioned, all or part of example blocks 402, 404 and406 may be performed as part of a passive scanning operation performedby the mobile device, and/or all or part of example blocks 408, 410 and412 may be performed as part of an active probing operation performed bythe mobile device. In certain instances, a plurality of passive scanningoperations may occur prior to an active probing operation, and/or inbetween two active probing operations. Conversely, in certain instances,two or more active probing operations may be performed without anyintervening passive scanning operations. Furthermore, as mentioned, incertain instances, a passive scanning operation and/or an active probingoperation may be affected in some manner in response to certain eventsand/or the like.

As presented by the example implementations described herein, a mobiledevice may perform a passive scanning operation for wireless signalsfrom wireless transceivers. In performing an example passive scanningoperation, a mobile device may acquire one or more signals transmittedby a wireless transceiver and determine at least an identity of thewireless transceiver (e.g., a MAC address, etc.), and measure a receivedsignal strength. Given limited transmission power at a mobile device(e.g., to extend battery charge life), a mobile device may transmitsignals applying a lower transmission power than applied at a fixedwireless transceiver for transmitting similar signals. As such, atransmission range or applicable coverage area of a wireless transceiverpositioned at a fixed location is typically greater than that of amobile device.

In certain example implementations, it may be presumed that, at leastfor short durations time, conditions in a signal path between a wirelesstransceiver and a mobile device affecting attenuation of a passivelyscanned wireless signal acquired at the mobile device (e.g., range,physical obstructions, etc.) similarly affect attenuation of a probesignal that may be subsequently transmitted from the mobile device tothe transceiver. In attempting to measure ranges to transceivers basedon round trip times, a mobile device may tailor the transmission powerof a probe packet to be transmitted to transceivers detected/identifiedin a passive scan based, at least in part, on a signal strength measuredfrom the passive scan. This may, for example, allow a mobile device toconserve battery life by transmitting one or more probe signals to oneor more wireless transceivers at less than a full transmission powerwhile still providing a sufficient signal strength to allow acquisitionof the probe packet by the most distant wireless transceivers beingprobed (e.g., those identified in a subset of wireless transceivers).

Thus, in certain example implementations, a transmission power for aprobe signal may be based, at least in part, on a received signalstrength measurement of a wireless signal acquired in a passive scanningoperation. In one particular example, a transmission power for a probesignal may be determined based, at least in part, on a lowest or minimumreceived signal strength measurement of wireless signals acquired in thepassive scanning operation from among wireless transceivers within thesubset of wireless transceivers to be probed. In other words, thetransmission strength for a probe signal being transmitted to a wirelesstransceiver associated with the signal path with the most attenuation(e.g., at the longest range, most interfering objects, etc.) may besufficient to allow that wireless transceiver to acquire the probesignal, without wastefully transmitting such a probe signal at a highertransmission power. Moreover, the same transmission power setting may beused for transmitting other probe signals to other wireless transceiversidentified in the subset of wireless transceivers to be probed.

In certain example implementations, a mobile device may not transmit aprobe packet to all wireless transceivers detected/identified in apassive scan. Here, for example as previously mentioned, a mobile devicemay select (e.g., three, four or five, depending on desired position fixaccuracy, for example) from several wireless transceiversdetected/identified in a passive scan. In one example, a mobile devicemay select from among the detected/identified wireless transceiverstransmitting wireless signals having the highest received signalstrength measurements in a passive scan. In certain instances, a mobiledevice may select a subset of wireless transceivers transmitting signalshaving a received signal strength that is acceptable, and adequate(threshold) angular separation from one another (e.g., as determinedfrom the vantage point of a rough estimate of location of the mobiledevice). In certain example implementations, as mentioned, one or morewireless transceivers may be selected so as to provide a low or minimumdilution of precision in a location estimate to be computed bycalculated ranges to the selected wireless transceivers.

The methodologies described herein may be implemented by various meansdepending upon applications according to particular features and/orexamples. For example, such methodologies may be implemented inhardware, firmware, and/or combinations thereof, along with software. Ina hardware implementation, for example, a processing unit may beimplemented within one or more application specific integrated circuits(ASICs), digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), processors, controllers, micro-controllers,microprocessors, electronic devices, other devices units designed toperform the functions described herein, and/or combinations thereof.

In the preceding detailed description, numerous specific details havebeen set forth to provide a thorough understanding of claimed subjectmatter. However, it will be understood by those skilled in the art thatclaimed subject matter may be practiced without these specific details.In other instances, methods and apparatuses that would be known by oneof ordinary skill have not been described in detail so as not to obscureclaimed subject matter.

Some portions of the preceding detailed description have been presentedin terms of algorithms or symbolic representations of operations onbinary digital electronic signals stored within a memory of a specificapparatus or special purpose computing device or platform. In thecontext of this particular specification, the term specific apparatus orthe like includes a general purpose computer once it is programmed toperform particular functions pursuant to instructions from programsoftware. Algorithmic descriptions or symbolic representations areexamples of techniques used by those of ordinary skill in the signalprocessing or related arts to convey the substance of their work toothers skilled in the art. An algorithm is here, and generally, isconsidered to be a self-consistent sequence of operations or similarsignal processing leading to a desired result. In this context,operations or processing involve physical manipulation of physicalquantities. Typically, although not necessarily, such quantities maytake the form of electrical or magnetic signals capable of being stored,transferred, combined, compared or otherwise manipulated as electronicsignals representing information. It has proven convenient at times,principally for reasons of common usage, to refer to such signals asbits, data, values, elements, symbols, characters, terms, numbers,numerals, information, or the like. It should be understood, however,that all of these or similar terms are to be associated with appropriatephysical quantities and are merely convenient labels. Unlessspecifically motion stated otherwise, as apparent from the followingdiscussion, it is appreciated that throughout this specificationdiscussions utilizing terms such as “processing,” “computing,”“calculating,” “determining”, “establishing”, “obtaining”,“identifying”, “applying,” and/or the like refer to actions or processesof a specific apparatus, such as a special purpose computer or a similarspecial purpose electronic computing device. In the context of thisspecification, therefore, a special purpose computer or a similarspecial purpose electronic computing device is capable of manipulatingor transforming signals, typically represented as physical electronic ormagnetic quantities within memories, registers, or other informationstorage devices, transmission devices, or display devices of the specialpurpose computer or similar special purpose electronic computing device.In the context of this particular patent application, the term “specificapparatus” may include a general purpose computer once it is programmedto perform particular functions pursuant to instructions from programsoftware.

The terms, “and”, “or”, and “and/or” as used herein may include avariety of meanings that also are expected to depend at least in partupon the context in which such terms are used. Typically, “or” if usedto associate a list, such as A, B or C, is intended to mean A, B, and C,here used in the inclusive sense, as well as A, B or C, here used in theexclusive sense. In addition, the term “one or more” as used herein maybe used to describe any feature, structure, or characteristic in thesingular or may be used to describe a plurality or some othercombination of features, structures or characteristics. Though, itshould be noted that this is merely an illustrative example and claimedsubject matter is not limited to this example.

While there has been illustrated and described what are presentlyconsidered to be example features, it will be understood by thoseskilled in the art that various other modifications may be made, andequivalents may be substituted, without departing from claimed subjectmatter. Additionally, many modifications may be made to adapt aparticular situation to the teachings of claimed subject matter withoutdeparting from the central concept described herein.

Therefore, it is intended that claimed subject matter not be limited tothe particular examples disclosed, but that such claimed subject mattermay also include all aspects falling within the scope of appendedclaims, and equivalents thereof.

What is claimed is:
 1. A method comprising, with a mobile device:acquiring signals from a plurality of wireless transceivers; identifyingeach of said plurality of wireless transceivers based, at least in part,on one or more of said acquired signals; determining a received signalstrength measurement for each of said plurality of wireless transceiversbased, at least in part, on one or more of said acquired signals; anddetermining a transmission power of a probe signal to be transmitted toat least one of said plurality of wireless transceivers based, at leastin part, on at least one of said received signal strength measurements.2. The method as recited in claim 1, and further comprising with saidmobile device: selecting a subset of wireless transceivers of saidplurality of wireless transceivers to receive said probe signal; anddetermining said transmission power of said probe signal based, at leastin part, on a lowest received signal strength measurement for saidsubset of wireless transceivers.
 3. The method as recited in claim 2,and further comprising with said mobile device: transmitting said probesignal to at least one of said subset of wireless transceivers at afirst time; acquiring a response to said probe signal from said at leastone of said subset of wireless transceivers at a second time; andcomputing a range to said at least one of said subset of wirelesstransceivers based, at least in part, on said first time and said secondtime.
 4. The method as recited in claim 3, and further comprising withsaid mobile device: computing an estimated location of the mobile devicebased, at least in part, on said range.
 5. The method as recited inclaim 3, wherein said range is based on a round trip time determinedbased, at least in part, on said first time and said second time.
 6. Themethod as recited in claim 2, wherein selecting said subset of wirelesstransceivers further comprises with said mobile device: selecting atleast two wireless transceivers of said subset of wireless transceiversbased, at least in part, on an angular separation between said at leasttwo wireless transceivers from a vantage point of an approximatelocation of said mobile device exceeding an angular threshold value. 7.The method as recited in claim 6, wherein said angular threshold valueis based, at least in part, on a dilution of precision (DOP) thresholdvalue for an estimated location of said mobile device.
 8. The method asrecited in claim 6, wherein said angular threshold value is based, atleast in part, on a threshold number of wireless transceivers withinsaid subset of wireless transceivers.
 9. The method as recited in claim2, wherein selecting said subset of wireless transceivers furthercomprises with said mobile device: selecting at least a threshold numberof wireless transceivers for said subset of wireless transceivers. 10.The method as recited in claim 9, wherein said threshold number ofwireless transceivers is based, at least in part, on a DOP thresholdvalue for an estimated location of said mobile device.
 11. An apparatusfor use in a mobile device, the apparatus comprising: means foracquiring signals from a plurality of wireless transceivers; means foridentifying each of said plurality of wireless transceivers based, atleast in part, on one or more of said acquired signals; means fordetermining a received signal strength measurement for each of saidplurality of wireless transceivers based, at least in part, on one ormore of said acquired signals; and means for determining a transmissionpower of a probe signal to be transmitted to at least one of saidplurality of wireless transceivers based, at least in part, on at leastone of said received signal strength measurements.
 12. The apparatus asrecited in claim 11, and further comprising: means for selecting asubset of wireless transceivers of said plurality of wirelesstransceivers to receive said probe signal; and wherein said means fordetermining said transmission power of said probe signal is based, atleast in part, on a lowest received signal strength measurement saidsubset of wireless transceivers.
 13. The apparatus as recited in claim12, and further comprising: means for transmitting said probe signal toat least one of said subset of wireless transceivers at a first time;means for acquiring a response to said probe signal from said at leastone of said subset of wireless transceivers at a second time; and meansfor computing a range to said at least one of said subset of wirelesstransceivers based, at least in part, on said first time and said secondtime.
 14. The apparatus as recited in claim 13, and further comprising:means for computing an estimated location of the mobile device based, atleast in part, on said range.
 15. The apparatus as recited in claim 13,wherein said range is based on a round trip time determined based, atleast in part, on said first time and said second time.
 16. Theapparatus as recited in claim 12, and further comprising: means forselecting at least two wireless transceivers of said subset of wirelesstransceivers based, at least in part, on an angular separation betweensaid at least two wireless transceivers from a vantage point of anapproximate location of said mobile device exceeding an angularthreshold value.
 17. The apparatus as recited in claim 16, wherein saidangular threshold value is based, at least in part, on a dilution ofprecision (DOP) threshold value for an estimated location of said mobiledevice.
 18. The apparatus as recited in claim 16, wherein said angularthreshold value is based, at least in part, on a threshold number ofwireless transceivers within said subset of wireless transceivers. 19.The apparatus as recited in claim 12, and further comprising: means forselecting at least a threshold number of wireless transceivers for saidsubset of wireless transceivers.
 20. The apparatus as recited in claim19, wherein said threshold number of wireless transceivers is based, atleast in part, on a DOP threshold value for an estimated location ofsaid mobile device.
 21. A mobile device comprising: a processing unitto: identify each of a plurality of wireless transceivers based, atleast in part, on one or more signals acquired from said plurality ofwireless transceivers; determine a received signal strength measurementfor each of said plurality of wireless transceivers based, at least inpart, on at least one of said one or more signals acquired from saidplurality of wireless transceivers; and determine a transmission powerof a probe signal to be transmitted to at least one of said plurality ofwireless transceivers based, at least in part, on at least one of saidreceived signal strength measurements.
 22. The mobile device as recitedin claim 21, said processing unit to further: select a subset ofwireless transceivers of said plurality of wireless transceivers toreceive said probe signal; and determine said transmission power of saidprobe signal based, at least in part, on a lowest received signalstrength measurement for said subset of wireless transceivers.
 23. Themobile device as recited in claim 22, and further comprising: acommunication interface, and wherein said processing unit to further:initiate transmission of said probe signal via said communicationinterface to at least one of said subset of wireless transceivers at afirst time; obtain a response to said probe signal from said at leastone of said subset of wireless transceivers at a second time via saidcommunication interface; and compute a range to said at least one ofsaid subset of wireless transceivers based, at least in part, on saidfirst time and said second time.
 24. The mobile device as recited inclaim 23, said processing unit to further: compute an estimated locationof the mobile device based, at least in part, on said range.
 25. Themobile device as recited in claim 23, wherein said range is based on around trip time determined based, at least in part, on said first timeand said second.
 26. The mobile device as recited in claim 22, saidprocessing unit to further: select at least two wireless transceivers ofsaid subset of wireless transceivers based, at least in part, on anangular separation between said at least two wireless transceivers froma vantage point of an approximate location of said mobile deviceexceeding an angular threshold value.
 27. The mobile device as recitedin claim 26, wherein said angular threshold value is based, at least inpart, on a dilution of precision (DOP) threshold value for an estimatedlocation of said mobile device.
 28. The mobile device as recited inclaim 26, wherein said angular threshold value is based, at least inpart, on a threshold number of wireless transceivers within said subsetof wireless transceivers.
 29. The mobile device as recited in claim 22,said processing unit to further: select at least a threshold number ofwireless transceivers for said subset of wireless transceivers.
 30. Themobile device as recited in claim 29, wherein said threshold number ofwireless transceivers is based, at least in part, on a DOP thresholdvalue for an estimated location of said mobile device.
 31. An articlefor use by a mobile device, the article comprising: a non-transitorycomputer readable medium having computer implementable instructionsstored therein that are executable by a processing unit in said mobiledevice to: initiate acquisition of signals from a plurality of wirelesstransceivers; identify each of said plurality of wireless transceiversbased, at least in part, on one or more of said acquired signals;determine a received signal strength measurement for each of saidplurality of wireless transceivers based, at least in part, on one ormore of said acquired signals; determine a transmission power of a probesignal to be transmitted to at least one of said plurality of wirelesstransceivers based, at least in part, on at least one of said receivedsignal strength measurements.
 32. The article as recited in claim 31,said computer implementable instructions being further executable bysaid processing unit to: select a subset of wireless transceivers ofsaid plurality of wireless transceivers to receive said probe signal;and determine said transmission power of said probe signal based, atleast in part, on a lowest received signal strength measurement for saidsubset of wireless transceivers.
 33. The article as recited in claim 32,said computer implementable instructions being further executable bysaid processing unit to: initiate transmission of said probe signal toat least one of said subset of wireless transceivers at a first time;initiate acquisition of a response to said probe signal from said atleast one of said subset of wireless transceivers at a second time; andcompute a range to said at least one of said subset of wirelesstransceivers based, at least in part, on said first time and said secondtime.
 34. The article as recited in claim 33, said computerimplementable instructions being further executable by said processingunit to: compute an estimated location of the mobile device based, atleast in part, on said range.
 35. The article as recited in claim 33,wherein said range is based on a round trip time determined based, atleast in part, on said first time and said second time.
 36. The articleas recited in claim 32, said computer implementable instructions beingfurther executable by said processing unit to: select at least twowireless transceivers of said subset of wireless transceivers based, atleast in part, on an angular separation between said at least twowireless transceivers from a vantage point of an approximate location ofsaid mobile device exceeding an angular threshold value.
 37. The articleas recited in claim 36, wherein said angular threshold value is based,at least in part, on a dilution of precision (DOP) threshold value foran estimated location of said mobile device.
 38. The article as recitedin claim 36, wherein said angular threshold value is based, at least inpart, on a threshold number of wireless transceivers within said subsetof wireless transceivers.
 39. The article as recited in claim 32, saidcomputer implementable instructions being further executable by saidprocessing unit to: select at least a threshold number of wirelesstransceivers for said subset of wireless transceivers.
 40. The articleas recited in claim 39, wherein said threshold number of wirelesstransceivers is based, at least in part, on a DOP threshold value for anestimated location of said mobile device.